652 X. VITAMINS D 



labeled vitamin D, that most of the missing vitamin D is excreted via the 

 intestine, not as an active vitamin, however, but as an mactive deriva- 

 tive.^"* It is not known whether this ingested vitamin D was inactivated 

 in the gastrointestinal tract, or whether it was absorbed michanged from 

 the tract, to be inactivated in the body and reexcreted into the intestinal 

 tract. 



There are several factors which are known to influence the absorption of 

 vitamins D from the small intestine. In the first place, Ivnudson and 

 Floody^"^ demonstrated that fat improved the utihzation of the anti- 

 rachitic vitamin. Thus, the extent of healing of rickets in rats was greater 

 when a known amount of vitamin D was given in conjunction with a diet 

 containing 5% of fat than when a fat-free regimen was employed. It was 

 noted that better results were obtained when the diets contained 10 or 20% 

 of fat than when fat-free diets were given, although the results were less 

 satisfactory than when the rations contained 5% of fat. It was not possible 

 to determine whether the improvement in the utilization of vitamin D in 

 the fat series was to be ascribed to a better absorption, or to some effect 

 on the vitamin D after absorption. Boer-"^ likewise reported that rachito- 

 genic diets no longer produced rickets when 10% of the saponifiable frac- 

 tion of margarine was added; he interpreted this as evidence that fat 

 exerts a sparing action on vitamin D. Kon and Booth^^" also produced 

 evidence to substantiate this conclusion. Finally, McDougall^^^ observed 

 that, when 11% of lard or olive oil was added to a low-calcium diet, the 

 rats no longer developed rickets. 



A second requirement for effective absorption of the vitamins D is bile. 

 Thus, the presence of this secretion is required in the case of the vitamins 

 D, as in that of the other fat-soluble vitamins and actually of fat itself. 

 Diittmann^'^ found that, when bile was absent from the gastrointestinal 

 tract of man and of other animals, osteoporotic malacia developed, due to 

 acidotic disturbance of the calcium metabohsm and of the digestion of fat, 

 Avith resultant lack of absorption of vitamin D. Seifert^^* suggested that 

 vitamin D is not absorbed in the absence of bile, and that therefore the 

 utilization of calcium in the intermediary metabolism is decreased. This 

 abnormal condition can be alleviated by the parenteral administration of 



208 A. Knudson and R. J. Floody, /. Nutrition, 20, 317-325 (1940). 



209 J. Boer, Ada Brevia Neerland. Physiol. Pharmacol. Microbiol, 9, 67-68 (1939). 



210 S. K. Kon and R. G. Booth, Biochem. J., 28, 111-120, 121-130 (1934). 



211 E. J. McDougall, Biochem. J., 32, 194-202 (1938). 



212 G. Duttmann, Brun's Beitr. klin. Chir., 139, 720-729 (1927). 



213 E. Seifert, Brun's Beitr. klin. Chir., 136, 496-498 (1926). 



